A tire has a laminated structure of carcass plies and belts, which are fiber or metallic cord members each coated with rubber. As a result, if an excessive load works in the adhesion areas of those members during vehicular travel, a phenomenon called “socketing” can occur in which cord ends and coating rubber separate from each other to cause cracks in the rubber. If the socketing occurring at various circumferential points of a tire are allowed to link together, they will cause a separation of the laminated members from each other.
If the separation spreads circumferentially or axially in the tire, there will be increased chances of tire burst occurring during vehicular travel.
Hence, it is desired that a technology be developed for detecting any separation early and warning the driver of an imminent tire burst before it occurs.
There are various methods proposed in the art for detecting internal failures, such as separations, of tires. In one of them (see Patent Document 1, for instance), a temperature sensor is embedded in the shoulder area which is prone to internal failures of the tire. Then the temperatures of the tire during vehicular travel are measured, and an internal failure of the tire is detected from the change in the temperature. This method makes use of temperature rise near the point of failure due to the local heating resulting from an internal failure of a tire. More specifically, an internal failure of a tire is detected by detecting a temperature rise in the tread before any peeling (separation) occurs.
In another proposed method for detecting internal failures of a tire (see Patent Document 2, for instance), temperature-sensitive ferrite pieces having a Curie point in a predetermined temperature range are disposed at a predetermined pitch along the circumference of the annular portion of a tire. Also, installed on the vehicle body side are a magnet forming an annular magnetic path intersecting with the annular portion of the tire and a coil wound around the outer periphery of the annular magnetic path. And electromotive forces excited in the coil by the changes in flux density associated with the revolution of the tire are measured, and deformation in the shoulder area of the tire is indirectly detected from the measured waveform, thereby detecting an internal failure of the tire.